Method for bleaching textile fabrics containing portions dyed with a sensitive dyestuff

ABSTRACT

TEXTILE FABRICS CONTAINING PORTIONS DYED WITH A SENSITIVE DYESTUFF SUCH AS A VAT DYE, A NAPHTHOL DYE OR CERTAIN COPPER PHTHALOCYANINE DYES, ARE BLEACHED BY SUBJECTING THE FABRIC TO THE ACTION OF A BLEACHING SOLUTION CONTAINING A PEROXYMONOSULFATE, WHICH SOLUTION IS BUFFERED AT A PH OF 5 TO 8.5, PREFERABLY A PH OF 5.5 TO 7. BLEACHING TEMPERATURES UP TO ABOUT THE BOILING POINT OF WATER ARE USABLE. PREFERABLY, THE FABRIC IS SATURATED WITH SUCH A SOLUTION AND THEN BLEACHED IN THE SATURATED STATE.

XR 3556710 EX' United States PatentOfice 3,556,710 Patented Jan. 19,1971 Int. Cl. D06l 3/02 US. Cl. 8-111 8 Claims DeL, assignor Wilming-ABS'I'RACT OF THE DISCLOSURE Textile fabrics containing portions dyedwith a sensitive dyestufi such as a vat dye, a naphthol dye or certaincopper phthalocyanine dyes, are bleached by subjectingthe fabric to theaction of a bleaching solution containing a peroxymonosulfate, whichsolution is buffered at a pH of 5 to 8.5, preferably a pH of 5.5 to 7.Bleaching temperatures up to about the boiling point of water areusable. Preferably, the fabric is saturated with such a solution andthen bleached in the saturated state.

BACKGROUND OF THE INVENTION The bleaching of textile fabrics containingportions dyed with a sensitive dyestuff has long been a problem. Forexample, when cellulosic fabrics containing portions dyed with naphtholdyes are bleached, the dyes' have a marked tendency to bleed andmark-off onto the undyed portions of the fabric or onto other goods intowhich they may come into contact during bleaching. The tendency of suchdyed portions to stain or mark-off is aggravated by severe bleachingconditions, particularly high temperatures, high alkalinities andextended bleaching times. Accordingly, mild bleaching conditions havebeen considered essential.

' It has been proposed to bleach fabrics containing portion dyed withsensitive dyestuffs under mild conditions,

e.g., at temperatures no higher than about 160 F. and pH values of from6.5 to 10, is contrasted with the more severe bleaching conditions oftemperatures of around 210 F. and pH conditions exceeding pH 10, such asare commonly employed when bleaching undyed cotton fabrics. Under suchmilder bleaching conditions, bleaching times of from about one-half toeight hours or more have generally been necessary. Patents indicatingsuch prior practices are Kauifman U.S. Pat. 2,391,700 and Smollens US.Pat. 3,280,039. It has also been suggested (Prett et al. US. Pat.3,227,655) that fabrics containing portions dyed with vat or naphtholdyes may be bleached with peracetic acid solutions at a pH of 4.5 to 6and at temperatures of 60 to 90 C. However, the use of peracetic fibersmade by processes employing manganese compounds as polymerizationcatalysts.

Thus, there is a need in the textile industry for a simple process,preferably one that can be practiced continuously, for bleaching fabricscontaining portions dyed with various sensitive dyes without requiringthe subjection of the fabric to severe bleaching conditions and withoutincurring dye bleeding, staining, or mark-0E onto the undyed'portions ofthe fabric, and without incurring discoloration of polyester fiberscontaining residual manganese compounds. The present invention isdirected to a process satisfying such a need.

SUMMARY OF THE INVENTION A method for bleaching textile fabricscontaining portions dyed with a sensitive dyestutf involving subjectingsuch a fabric to the action of a bleaching solution comprising anaqueous solution of a peroxymonosulfate at a concentration to providefrom 0.005% to -l% active oxygen, which solution contains a bufferingagent effective to maintain the pH of the solution at a value within therange 5 to 8.5. Preferably, the fabric is saturated with such a solutionand the saturated fabric is then heated, e.g., by steam, for a time offrom 5 minutes to 20 hours to effect the bleaching.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS The bleaching solutionemployed in practicing the method of the invention is an aqueoussolution containing a peroxymonosulfate in an amount such as willprovide in the solution a concentration of active oxygen of from 0.005to 1%. Any of the water soluble peroxymonosulfates such as the alkalimetal peroxyfinonosulfates, ammonium peroxymonosulfate or the alkalineearth metal peroxymonosulfates, can be employed. The most preferredperoxymonosulfate is the potassium peroxymonosulfate triple saltcompound of the formula KHSO; K 50 2KHSO A product comprising suchtriple salt compound and containing about 4.7% active oxygen by weightis 'available commercially. The peroxymonosulfate component of thesolution can also be formed in situ in the solution by the reaction ofperoxymonosulfuric acid, also called Caros acid, H 50 and an alkali suchas caustic soda,

caustic potash, ammonium hydroxide or an alkaline salt such as sodium orpotassium carbonate, or the like. Preferably, the concentration in thesolution of active oxygen derived from the peroxymonosulfate will rangefrom 0.005 to 0.02% for immersion bleaching, and from 0.03 to 0.2% forsaturation bleaching.

To be effective for the present purpose, the peroxymonosulfate bleachingsolution should be buffered to a pH within the range 5 to 8.5,preferably 5.5 to about 7. If the pH is lower than about pH 5, thesolution may be sufficiently acidic to damage cellulosic fabrics. On theother hand, if the solution has a pH substantially higher than about8.5, the solution becomes less stable. When the pH of the solution isbuffered over the entire bleaching period to a value within the rangestated, excellent bleaching of the undyed portions of the fabric, i.e.,the white background portions, occurs with little or no bleeding of dyesfrom the dyed portions resulting and, consequently, with little or nostaining of the undyed portions or mark-off onto such undyed portions.

The commercially available peroxymonosulfate triple salt product isquite acidic so that solutions thereof will generally require at leastpartial neutralization with an alkaline material in order to bring thepH of the solution within the range pH to 8.5, most preferably 5.5 to 7.Such adjustment of the pH can be effected by the addition of any of thecommon alkalies such as sodium, ammonium or potassium hydroxide, orvarious alkaline salts, but it is also generally desirable that a salthaving buffering properties such as to maintain the pH within such arange during the entire bleaching operation be also present. The alkalimetal phosphates, particularly tetraalkali metal pyrophosphates such astetrasodium pyrophosphate, are particularly effective for this purposealthough other buffering agents such as sodium bicarbonate, thecombination of borax and phosphoric acid or of tetrasodium pyrophosphateand sodium acetate may also be used.

Although bleaching with such solutions may be effected at ordinarytemperatures, it generally will be preferred to employ somewhat elevatedtemperatures in order to de- Crease the bleaching time required. Thus,bleaching will generally be-effected at a temperature of at least 100F., e.g., temperatures from 100 F. up to as high as about 212 F. At suchtemperatures, bleaching times ranging from about minutes to 5 hours maybe employed, the higher temperatures generally requiring shorter timesthan lower temperatures. Bleaching may be effected by immersing thefabric in the bleaching solution maintained at the desired temperature,but preferably the fabric will be impregnated or saturated with anamount of the bleaching solution equal to from about 50% to 150%,preferably 80-120%, of the fabric weight, and the saturated fabric willthen be heated at the desired temperature, e.g., by contacting it withlive steam or a mixture of steam and air, depending upon the temperaturedesired. Most pref- The invention is illustrated by the followingexamples in which all compositions expressed as percentages are byweight. Unless otherwise stated, the fabric samples employed in theexamples were in tightly braided form and each sample was saturated withthe designated bleaching solution and the saturated sample was thenbleached in a chamber containing live steam or a mixture of live steamand air to get temperatures above 175 F., or placed in a covered beakerimmersed in a water bath maintained at the desired bleach temperature toget temeratures below 175 F. Following bleaching, the samples wereunbraided and rinsed well with hot water at least three times.

The following abbreviations are used in some of the examples todesignate certain of the constituents of the bleaching solutionsemployed: DTPA designates a commercial diethylenetriaminepentaaceticacid sequesterant; TSPP designates tetrasodium pyrophosphatedecahydrate; and PMS designates the commercially available potassiumperoxymonosulphate product comprising the triple salt KHSO -K SO -2KHSOhaving an active oxygen content of about 4.7%. Bleaching solutionscontaining peracetic acid were formulated using the commerciallyavailable peracetic acid solution.

EXAMPLE 1 Samples of a cotton-polyester (ethylene glycol terephthalate)shirt fabric containing red stripes formed of yarns dyed with reddisperse and naphthol red dyes, and black stripes formed of yarns dyedwith black disperse and black vat dyes, woven into the fabric werebleached using the bleach solutions indicated in the tabulation below.Before bleaching, the fabric samples had been scoured by saturating themwith an aqueous solution containing 0.83% TSPP and 0.5% soda ash, andthen heating the saturated fabric at 150 F. for minutes. The resultsobtained were as follows:

Run

Bleach solution Bleeding or Bleach conditions mark-off 1.26% sodiumsilicate 0.80% peracetic acid... 0.40% TSPP pH 5.8 (NaOH) 1.0% PMS pH7.0 (NBOH) I lhour at 212 F Considerable.

Visible but 1858 .::}30 minutes at 210 F than in A.

erably, a continuous length of the fabric to be bleached will becontinuously saturated with the bleaching solution, following which thesaturated fabric will be continuously heated by contact with steam or amixture of steam and air and the heated fabric then stored, e.g., in aJ-box or other equipment, from which it can be continuously withdrawnafter a residence therein equal to the desired bleaching time.

The method of the invention is applicable to the bleaching of fabricscontaining portions dyed with naphthol dyes, disperse dyes, vat dyes andcopper phthalocyanine dyes. It is also applicable to fabrics containingone or more of the above type dyes and, thus, avoids the necessity ofsegregating differently dyed fabrics during bleaching. The process issuitable for bleaching the fabric in open width or rope form in thewidely used continuous bleach J-box ranges with no significantmodification of the equipment being required. Although continuousoperation is most generally preferred, the method of the invention canbe practiced in batch operations when desired.

Only a short bleaching time was required in Run C because essentiallyall of the active oxygen of the PMS salt was used up in that time. Allof the samples were wellbleached, but the data show that only in thecase of those bleached with the PMS bleaching solution did bleachingoccur without causing the dye to bleed or mark-off onto the undyedportions of the fabric.

EXAMPLE 2 Samples of a light weight, all-cotton fabric containing aone-half inch check pattern dyed with a blue copper phthalocyanine dyewere bleached with the bleaching solutions indicated in the followingtabulation. White threads were pulled from each bleached sample and theextent of dye bleeding was assessed by observing the relative bluecoloration of the white threads. The data tabulated below show that dyebleeding occurred to a significant extent when using the hydrogenperoxide or peracetic acid bleach solutions but did not occur to anysignificant extent when using the PMS type bleach solutions.

Run Bleach solutions Bleach conditions Relative coloration 01 whitethreads 1.5% sodium silicate ..}60 minutes at 210 F-- Slight blue hue.

Born! ..}....do pH 6.2

{2.5 cc. 0l86%H4PO 1.2% PMS.-. D 2.0% TSPP...

pH 6.0 (BQPO) 0.23% peraoetic acid 2.0% sodium acetatetrihydrate........

} 0.2% TSPP pH 5.8 (NaOH) {1.2% PMS 2.0% sod l um acetate tripHd It isnoteworthy that even when the PMS bleach solution contained a higherconcentration of active oxygen than the otherwise similar peracetic acidbleach solution, (i.e., the PMS solution in Run F contained about 0.056%active oxygen whereas the peracetic acid solution in Run E containedabout 0.048% active oxygen), the amount of dye bleeding was less withthe PMS solution than with the peracetic acid solution. When the entirefabric samples were viewed, those bleached with the PMS solution haddistinctly cleaner looking background portions than did those bleachedwith the other solutions.

When the general procedure of the above examples was followed inbleaching samples of a 50:50 cotton/ polyester fabric having a redchecked pattern (A checks) containing disperse and naphthol red dyes,and the dye bleeding that occurred wasassessed by observing therelatively pink coloration of white threads pulled from the bleachedsamples, it was noted that white threads from the samples bleached withalkaline peroxide solutions and pcracetic acid solutions had visiblymore pink coloration than did the white threads pulled from samplesbleached with PMS solutions. Viewing the whole fabric samples, thosebleached with PMS solutions had distinctly whiter looking backgroundareas than did the samples that were bleached with alkaline peroxide orperacetic solutions.

EXAMPLE 3 Fabric samples similar to those in Example 2 were sat uratedwith a solution containing 1% PMS, 0.5% ,TSPP and 2% sodium acetatetrihydrate (pH 6.4) and bleached either at 120 F. for one hour in 2stages or at 150 F. for 1 hour in a single stage. All of the sampleswere well bleached and there was no visible evidence of dye bleedingonto white background as compared to similar fabrics bleached witheither alkaline hydrogen peroxide or peracetic acid bleaching solutionsas indicated in the above tabulations.

EXAMPLE 4 This example illustrates bleaching in a continuous op eration.Five samples of various colored fabrics, each about 6 ft. x 10 in., werebutt-seamed together and the resulting assembly was butt-seamed into thecenter of a 100 yd. x 10 in. sample of unbleached, unscoured cottonfabric. The colored samples were: (a) a sample of the allcotton fabricused in Example 2, (b) a sample of the cotton/polyester fabric used inExample 2, (c) an all-cotton light-weight fabric having a 1-inch redchecked pattern dyed with naphthol red, (d) a medium weight all-cottonfabric having naphthol red stripes and yellow stripes against a broadwhite background, and (e) an all-cotton seersucker containingalternating A" white and green .}li5 minutes at 210 F.....-. Do;

...\20 minutes at 212 F Light blue hue.

\mdo None visible.-

stripes dyed with a vat green dye. The resulting fabric train wascontinuously saturated to about of its weight with a PMS bleachingsolution of the composition set forth in Example 3, then bleached bypassing it continuously through a J-box maintained at about 190 F. witha mixture of steam and air. The rate of travel of the fabric trainthrough the J-box was such as to give a residence time thereir't: forthe fabric of about 30 minutes. The bleached fabric withdrawn from theJ-box was washed by passing it through water at 180 F. following whichthe process was repe ted. All of the colored fabric samples in thetrainwere well-bleached and showed no evidence of bleeding or mark-offof the dye onto undyed portions of the fabric.

EXAMPLE 5 This example illustrates bleaching with a peroxymonosulfatesolution in accordance with the invention in a batch operation. Samplesof a cotton seersucker fabric weighing about 11 grams and containingalternating white and eitherstripes having yarns dyed with a vat bluedye or yarns dyed with a copper phthalocyanine dye, were bleached byimmersing the sa for one hour in a solution maintainedat 16010 180 F. ata'iiquorzgoods weight ratio of 10:1. The bleach solution contained 0.2%PMS, 0.5% TSPP and 0.3% acetic acid, and its pH had been adjusted to 6.2with caustic soda. The bleached samples had well-bleached whitebackgrounds which showed no visible n'ace of dye bleeding or mark-off.

The fabric bleached in the above example contained many motes, some ofwhich remained after the bleaching operation. This fabric was moredifficult to bleach than 'were the fabrics used in the other examplesand the fact EXAMPLE 6 Samples of a cotton-polyester shirt materialcontaining crisscrossing stripes of yarns dyed with either an orangedye, a gray dye or a naphthol red dye, were saturated with a bleachsolution containing 1% PMS, 2% TSPP, and 0.5 acetic acid, its pH havingbeen adjusted to 6.8 with caustic soda. The saturated samples were thenheated at 180 F. for 15 minutes. This bleaching treatment caused 7: dyebleeding or mark-off, nor any visible change in the color or hue of thedye.

i'tt't of the above bleached samples were again b eached for 45 minutesat 210 F. using a bleaching solution containing 0.5% H 1.5% sodiumsilicate and 0.05% Epsom salt, the pH of the solution being 104.Although the white background areas of the rehleached samples werewell-bleached, the color of the dyed areas had been changed from theoriginal bright red to a dull off-red. The remainder of the aboveoncebieached samples were bleached for minutes at 210 F. with a bleachsolution containing 1% PMS, 0.5% TSFP and 2% sodium acetate trihydrate,the pH of the solution being 6.4. The white background areas of theresulting twice-bleached samples were well-bleached and inc-re was novisible change in the color of the dyed areas.

EXAMPLE 7 Liquor: goods Bleach solution ratio Bleach conditions {l PMS2.0% sodium acetate trihymzl 150 F./1 hour.

pH 6.3 0.23% peraoetic 0.5% TSPP. pll 6.3 (NaOl-l). SamensRunA- il......SameasRunB 1:1 212 F./l5 minutes. 1:1 Do. I

The samples treated with the PMS solution (Runs A and f appearedessentially as white as the original untreated yarn, whereas the samplestreated with the peracetic acid solution (Runs B and D) had anObjectionable and distinct off-white cast. The results show that the PMStype bleach solution caused no significant discoloration of polyesterfibers, containing residual manganese catalysts, whereas the peraceticacid bleach solution caused a distinct and objectionable discoloration.These results are significant since although polyester fibers per seordinarily require little or no bleaching, such fibers are commonlyblended in fabrics with cotton fibers which do require bleaching so thatwhen blends of the-two types of fibers are. bleached, discoloration ofthe polyester fibers of the blend has the effect of decreasing thewhiteness of the rain-dyed portions of the fabric.

As indicated previously, the preferred peroxymonosulfate bleachsolutions for use in practicing the method of the invention are slightlyacidic. It might have been expected that such acidic solutions wouldhave a degrading effect upon cellulosic fabrics. It has been found,however, that no significant degradation of such fabrics occurs whenthey are bleached with the PMS solutions indicated in the examples underthe preferred pH conditions, i.e., pH 5.5 to 7. Thus, cotton fabricsbleached in single-stage operations under those conditions gave cuamvalues no higher than about 3. These are highly acceptable values sincea cuam fluidity not exceeding about 7 is generally consideredsatisfactory.

I claim:

1. A method of bleaching a textile fabric having por' tions thereof dyedwith a sensitive dyestufi, comprising subjecting said fabric to theaction of an aqueous bleaching solution consisting essentially of awater-soluble peroxymonosulfate at a concentration to provide from 0.005to 1% active oxygen and a buffering agent etiective to maintain the pHof the solution within the pH range of 5 to 8.5.

2. The method of claim 1 wherein the pH of the solution is 5.5 to 7.

3. The method of claim 1 wherein bleaching is effected by immersing thefabric in the bleaching solution at a temperature up to about 212 R,which solution contains 0.005 to 0.02% active oxygen.

4. The method of claim 1 wherein bleaching is effected by saturating thefabric with the bleaching solution containing 0.03 to 0.2% activeoxygen, and maintaining the saturated fabric at a temperature from F. toabout 212 Fffor from about 10 minutes to 5 hours.

5. The method of claim 1 wherein the fabric to be bleached has portionsdyed with a naphthol dye.

6. The method of claim 1 wherein the fabric to be bleached has portionsdyed with a vat dye.

7. The method of claim 1 wherein the fabric to be bleached has portionsdyed with a copper phthalocyanin'c dye.

8. The method of claim 4 wherein the fabric is continuously saturatedwith the bleaching solution, the saturated fabric is continuously heatedto a temperature of from 100 F. to about 212 F. and stored at saidtemperature for from about 10 minutes to about 5 hours.

References Cited UNITED STATES PATENTS 3,048,546 8/1962 Lake ct al.252186X 3,049,495 8/1962 Jenkins et al. 2S2-l86X MAYER WEINBLATT,Primary Examiner U.S. C1. X.R. 25295, 99

